Acoustic system



Dec. 26, E BOWLES ACOUSTIC SYSTEM Filed Oct. 12, 1929 jiu eiifoi' Ida/avail). Bow/es MM m afioi'iiw 50 sonance points determined by the resonances of tivity.

Patented Dec. 26, 1933 i A i V UNETED STATES PATENToOFFlCE ACOUSTIC SYSTEM; i A

Edward Lindley Bowles, Wellesley Farms,

- Mass.

Applicationoctober 12, 1929. Serial N0.'399,361

13 Claims. (o1. 178-'-44) The present invention relates to acoustic-elecof work. For example, let it be assumed, as is tric systems, and its chief object is to increase usually the case with apparatus of this type, that highly, for predetermined frequencies, the selec-' the impedance betweenthe points 18 and 19,1ooktivity and sensitivityof the diaphragms' or simiing'into the element 2, isinductive. A condenser 5 lar sound-energy-receiving parts of acoustic- 3 may, therefore, be connected, as shown, to perelectric pick-up systems. Other objects will be mit tuning to parallel resonance. This tuning, explained hereinafter, and will be particularly of course, since the mechanical and electrical pointed out in the appended claims. systems are coupled together, reflects back A feature of the invention contemplates reduce through the diaphragm 1. For the same reason,

ing the acoustic resistance or impedance of the any mechanical'property of the diaphragm l is diaphragm to a zero value, or to a very small reflected through into the element 2. Even with value, preferably by associating the diaphragm such condenser tuning, however, the voltage V with a vacuum-tube regenerative circuit element across the condenser terminals may not vary through an acoustic-electric circuit element capawidely enough with a change in frequency.

l5v ble of converting electric energy into acoustic According to the present invention, however, 70. energy, and vice versa. The diaphragm being the voltage across the condenser 3 is amplified, thus highly tuned at a single frequency by virtue and energy is regeneratively f d back to neuof the regenerative electric circuit element associtralize much of the inherent resistance which is ated therewith, it is highly selective and sensiintroduced intothe system by the resistance of v tive. The invention is applicable to sound-receivthe coil 8, through friction in the diaphragm, and 75. 7

'ing systems, to sound-reproducing units, like loud in other moving mechanical elements. To this speakers, so that they may be adapted to emit end, in the illustrated embodiment of the invena single frequency, electric-acoustic"analyzers tion, the system is connected with atwo-stage and filters, and to otheruses. I resistance-coupled amplifier 10, 11, and the re- 2 The invention will be explained in connection generative feed back mayibe effected by means with the accompanying drawing, in which Fig. 1 of an inductor coil 16, in the output circuit of is a diagrammatic view of apparatus'and circuits either the tube 10 01 the tube 11,coupled to the constructed and arranged according to a precoil 8,-or'by means of a variable coupling referred embodiment of the present invention; Fig. sistor 6. The output of the tube 11 is, of course,

0 2 is a similar view of a modification; and Fig. designed of the proper style to be set back through 85.

3 is a fragmentary view of another'modification. the resistor 6, or coil 16, to augment the voltage A diaphragm 1 is shown coupled'to-a mechaniupon the condenser 3. By the use of this regencal-electrical device 2 of any well known type. eration, a given small diaphragm l and mechani- Two types are illustrated in the-drawing, one an cal-electrical converting element 2 can be made 35 electro-magnetic converter (Figs. 1 and2) comto have a very selective characteristic and can prising an intermediately pivoted armaturelii cobe made to be very sensitive to sound waves of operating with acoil 8 and mechanically co'na given frequency. In fact. the system can be v n'ected with the diaphragm at 17, and the other made so sensitive to sound of a given frequency (Fig. 3) a moving-coil type of drive. Any other that the combination may be used asan analyzer 4J3v type of electro-"nechanical element may be used of sound waves, where the impinging waves may 95. in place of those illustrated. As ordinarily embe of various frequencies, but where the dia-' ployed, these devices are supplied with electric phragm will respond, to all intents and purposes, power from a suitable source to drive the diato but one of these Waves. The ratio of any phragms, but the operation is reversible, and given frequency to the resonance frequency may,

45 the mechanical vibrations of the diaphragm are in this manner, be greatly increased, sometimes here converted into electric energy. as much as twenty or thirty times or more. In-

The combination of the diaphragm 1 and the deed, the increase'is limited only by the unienergy-converting element Zordinarily yields an formity of the different elements of the appaacoustic-electric system that, though having re-.. ratus available and upon'the permissible sensithe mechanical and electrical elements of the A diaphragm orjpiston type of acoustic picksystem, does not have a single, sharp resonance up'is thus provided by the use of regeneration, as point above all others, unless electrically or me? described. that is far more sensitive ,to a given I chanically tuned, and even then,-these resonances frequency and. therefore. far less sensitive to .5 maynot be so sharp asdesirablefor certain types other frequencies, than is possible of attainment 110 with very much larger, and more cumbersome, systems at present in use, and the system of the present invention is. furthermore, far more practical than present-day systems. The diaphragm will, of course. vibrate at the articular frequency, since the resistance, as used acoustically, is zero. Such a condition actually exists in an electric circuit where the resistance is completely cancelled, as by using re eneration. If the acoustic element is associated with an acoustic network Where there are losses, however, it will be rendered stable, just as an electric circuit, that would otherwise oscillate, will not oscillate if it is connected in a circuit where the net resistance is positive.

The energy may be taken out of the system at terminals 20, 21 in the output circuit of a vacuum tube 12.

The principle of the present invention has also other uses, as in acoustic-wave filters. It is often as important to have non-dissipative acoustic elements in acoustic-wave filters as it is, in electric filters, to have nonedissipative circuit elements constituted, for example, of inductances and capacitances. t is possible to insert a system constructed according to the present invention in an electric-wave filter. so as to yield a dissipationless circuit at the particular frequency. If, for example, a sound wave is sent into a tube through one end to a diaphragm disposed at its other end, and if the diaphragm is tuned, in accordancewith the present invention, to the frequency of the impinging wave, the tube will act upon the wave as though it were continued on instead of being terminated at the point where the diaphragm is located.

Other modifications and changes will also occur to persons skilled in the art. and all such are considered to fall within the spirit and scope of the present invention. as defined in the appended claims.

What is claimed is:

1. Apparatus of the character described comprising, in combination, means responsive to receive sound energy overa range of predetermined frequencies, means connected with the soundenergy-receiving means for converting the sound energy into electric energy. means for tuning the converting means to receive sound energy of but a single frequency within the range, and a vacuum-tube device connected with the converting means.

2. Apparatus of the character described comprising, in combination, a vibratory diaphragm responsive to receive sound energy over a range of predetermined frequencies, means connected with the diaphragm for converting the sound energy into electric energy, means for tuning the converting means to a frequency within the range, and a vacuum-tube device regeneratively connected with the converting means.

3. Apparatus of the character described comprising, in combination, a vibratory sound-energy diaphragm having a range of predetermined frequencies, vacuum-tube apparatus, means connecting the diaphragm with the apparatus and capable of reversibly converting acoustic energy into electric energy, and means for tuning the last-named means so as to reversibly convert but a single frequency within the range, whereby the radiation efficiency of the diaphragm is increased to a very large value.

4'. A sound analyzer comprising, in combination, means for receiving sound energy over a range of predetermined frequencies, means connected with the sound-energy-receiving means for converting the sound energy into electric energy, a vacuum-tube device regeneratively connected with the converting means, and means for tuning the converting means to successive frequencies within the range to analyze the received sound. a

5. A filter comprising, in combination, means for receiving sound energy over a range of predetermined frequencies, means connected with the sound-energy-receiving means for converting the sound energy into electric energy, a vacuumtube device regeneratively connected withthe converting means, and means for tuning the converting means to filter out all except a predetermined frequency in the range.

6. Apparatus of the character described comprising, in combination, means for sending sound energy over a range of predetermined frequencies, means connected with the sound-energy-sencling means for converting electric energy into sound energy, means for tuning the converting means to a frequency within the range, whereby said frequency only will be transmitted, and a vacuum-tube device connected with the converting means.

7-. Apparatus of the character described comprising, in combination, a vibratory diaphragm capable of transmitting SOLllld energy over a predetermined range of frequencies, an accousticalelectrical converter connected with the diaphragm for converting electric energy into sound energy, means for tuning the converter to a frequency within the range, whereby said frequency only will be transmitted, and a vacuum-tube device 110 regeneratively connected with the converter.

8. Apparatus of the character described comprising, in combination, a vibratory diaphragm capable of transmitting sound energy over a predetermined range of frequencies, means connected 115 with the diaphragm for converting electric energy into sound energy, means for tuning the con-. verting means to a frequency within the range, whereby said frequency only will be transmitted, and a vacuum-tube device regeneratively connected with the converting means.

9. Apparatus of the character described comprising, in combination, sound-energy means responsive to a range of predetermined frequencies, means connected with the sound-energy 125 means for reversibly converting sound energy into electric energy, means for tuning the converting means to a frequency within the range, whereby said frequency only will be reversibly converted, and a vacuum-tube device connected 130 with the converting means.

10. Apparatus of the character described comprising, in combination, a vibratory diaphragm responsive to sound energy over a range of predetermined frequencies, a mechanical-electrical converter connected with the diaphragm for reversibly converting sound energy into electric energy, means for tuning the converting means to a frequency within the range, and a vacuumtube device regeneratively connected with the converter.

11. Apparatus of the character described comprising, in combination, a vibratory diaphragm responsive to sound energy over a range of predetermined frequencies, means connected with the diaphragm for reversibly convertingsound energy into electric energy, meansfor tuning the converting means to a frequency within the range, whereby said frequency only will be reversibly converted, and a vacuum-tube device vacuum-tube device regeneratively connected with the converting means, and means for tuningthe converting means to successive frequencies within the range to analyze the received sound. 13. A filter comprising, in combination, soundenergy means responsive to a range of predetermined frequencies, means connected with the sound-energy means for reversibly converting the sound energy into electric energy, a vacuumtube device regeneratively connected with the converting means, and means for tuning the converting meansto filter out all except a predetermined frequency in the range.

EDWARD L. BOWLES. 

